1. Technical Field of the Invention
The present invention relates to a lossless compression-encoding device and a decoding device for image data.
2. Description of the Related Art
Image data compression technologies can be mainly classified into lossy compression technologies and lossless compression technologies. lossy compression technologies mostly use orthogonal transformation and have an advantage in that they obtain a high compression ratio although it is not possible to completely reconstruct original image data from compressed data.
One example of lossless compression technology is JPEG-Lossless (JPEG-LS) of the Joint Photographic Experts Group (JPEG) which performs compression using both differential coding and variable-length coding. This type of lossless compression technology has an advantage in that it is possible to completely reconstruct original image data from compressed data although a high compression ratio is not obtained. Therefore, this lossless compression technology is used for purposes such as storage or exchange of medical images. One lossless compression technology is described in Japanese Patent Application Publication No. Heisei 9-37271.
A variety of image processing devices, which read and decode compressed data of an image of a sprite from a memory and which display the decoded sprite image on a monitor, have been provided. When there is a need to completely reconstruct the same sprite image as before compression, these image processing devices need to generate compressed data of a sprite image that is to be stored in a memory using the lossless compression technology and then to decode the compressed data read from the memory. However, the amount of the compressed data of the sprite image is large if the compressed data is generated using the lossless compression technology. Thus, it takes time to read compressed data required to decode the sprite image from the memory and it is not possible to transmit the compressed data to a decoder in the image processing device within a set period and thus it is not possible to display a sufficient amount of sprite image on a screen.